In a bowl, stir 2 tablespoons of the horseradish with the lemon juice, Worcestershire, celery seeds and 1/2 teaspoon of black pepper.,Whisk in 1/4 cup of the canola oil in a steady stream; season with salt.,Add the tomatoes and celery ribs and leaves, season with salt and pepper and toss.,In a small bowl, stir the sour cream with the remaining 2 tablespoons of horseradish.,______,Rub the remaining 2 tablespoons of canola oil all over the steak and season with salt and black pepper.,Grill the steak over moderately high heat, turning once, until nicely charred, 3 to 4 minutes per side for medium-rare.,Transfer the steak to a work surface and let rest for 5 minutes.,Slice the steak across the grain and serve with the tomato salad and horseradish cream.